(I should know better but) I'll try to answer this simply, with the usual caveat that I'm not a coach and have no sports science qualification, so the answer is based purely on my experience and reading over a few years.
Long rides in winter when you're building a base of endurance and aerobic fitness are useful things. During the race season, however, and assuming you've got limited time to spend on the bike each week, the following apply:-
-The body tends to hold on to endurance fitness longer than other sorts of higher-intensity fitness, so it needs "topping up" less frequently, and..
-Long rides drain the body of reserves and hence require recovery - possibly two days - before you can train hard again. That's two days when you can't do anything useful, and..
-The general advice is that for endurance ability during races you only need to train for the length of race you're doing, so if you're doing (say) 50-60 mile races, you only need to be doing similar distances for your longest endurance training rides.
So, at this time of year, most people who are racing will be doing maybe one long ride a week (hence the 3hr Saturday training ride) and the rest of the time doing more intense stuff - threshold work, sprints, tempo, hill intervals, etc. The more seriously long stuff you do, the less able you are to go to the limit on the more intense stuff (or the less time you have available to do it).
Incidentally, I've seen a fair bit of advice that completely emptying the tanks (in a crawling to the sweet shop kind of way) isn't helpful in training terms - largely because of the recovery load it puts on the body and the strain on the immune system. There seems to be evidence that training the body to burn fat on long rides is useful (I just use water or Nuun/Zero tabs in water on long winter rides) but the suggestion is to build this up steadily rather than ever get to the point where you can barely stand.
